Definition
The twisting force the engine applies to turn the propeller, and the equal twisting resistance the propeller produces against the engine as it moves through the air. In a turboprop, this is the rotational load the propeller places on the power section, measured and used as a primary indication of engine power output.
Plain English
It's the turning force between the engine and the propeller. The engine twists the prop one way; the prop, pushing against the air, resists that twist. How hard that twisting is happening tells you how much power the engine is producing.
Context Anchor
Seen on turboprop engine instruments and in power-setting discussions, especially when setting takeoff, climb, or cruise power.
Derivation
Torque comes from the Latin torquere, meaning to twist. It is literally a twisting force. In propeller systems, that twisting is what the engine does to the prop, and what the prop does back against the engine.
Why Pilots Care
Pilots must anticipate and correct the roll tendency with aileron input, especially during takeoff and high-power climbs, to maintain coordinated flight.
Analogy
It is like turning a bolt with a wrench. The important point is not just that the wrench is moving, but how much twisting force you are applying to it.
Intuition Check
Do not read “propeller torque” here as only the airplane’s tendency to roll or yaw from the spinning propeller. In this engine context, it means the twisting force and load being delivered to the propeller.
Example Sentence 1
On takeoff, the pilot advanced the power levers until propeller torque reached the value listed in the performance chart.
Example Sentence 2
When the pilot advanced power in the fixed-shaft turboprop, propeller torque produced an immediate left roll tendency.